Phylogeography and demographic history of the Andean degu,Octodontomys gliroides (Rodentia: Octodontidae)

The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhabiting pre‐Andean pre‐Puna and Puna environments of tropical South America. In order to understand the phylogeographic patterns of Octodontomys gliroides, we sequenced 579 bp of the mitochondrial DNA control region from 100 individuals collected from 20 populations across its entire distributional range. The phylogenetic and parsimony network, in conjunction with analysis of molecular variance (AMOVA), revealed a structured pattern of geographic differentiation of O. gliroides, with the occurrence of two well‐defined evolutionary lineages: lineage A, restricted to Bolivia and Chile, and lineage B, restricted mainly to Argentina. Analysis of population structure inferred three genetic clusters along the distribution of O. gliroides that mostly agree with the four major barriers inferred by BARRIER analysis (e.g. rivers, salt flats, deserts, and mountain systems). In addition to the significant differentiation found among all levels studied, a positive correlation was identified between genetic and geographic distance, similar to as expected under the isolation‐by‐distance model. The most recent common ancestor of O. gliroides was estimated as c. 5.99 Mya, and the divergence between lineages A and B is estimated to have occurred by the Middle Pleistocene, about 0.69 Mya. The mismatch distributions and neutrality tests suggested a signal of population range expansion for both lineages coincident with major climatic changes that occurred during the wet–dry events of the Pleistocene in the Andean Puna region. Bayesian skyline plots (BSPs) for lineage A suggest a long history of constant population size followed by a period of slight to moderate demographic expansion at c. 0.04 Mya, whereas lineage B remained unclear after BSP analysis, probably because of the limited sample size.     

Whole-genome duplications in South American desert rodents (Octodontidae)

The discovery of tetraploidy in the red viscacha rat, Tympanoctomys barrerae (4 n  = 102) has emphasized the evolutionary role of genome duplication in mammals. The tetraploid status of this species is corroborated here by in situ PCR and Southern blot analysis of a single-copy gene. The species meiotic configuration strongly suggests a hybrid derivation. To investigate the origin of T. barrerae further, the recently described Pipanacoctomys aureus was studied. This 92-chromosome species also has a duplicated genome size, redundant gene copy number and diploid-like meiotic pairing, consistent with an event of allotetraploidization. Phylogenetic analysis of mitochondrial sequences indicates sister-group relationships between these two tetraploid rodents. The new karyotypic data and the phylogenetic relationships suggest the participation of the ancestral lineages of Octomys mimax in the genesis of P. aureus . The high overall DNA similarity and shared band homology revealed by genomic Southern hybridization as well as matching chromosome numbers between O. mimax and the descendant tetraploid species support the notion of introgressive hybridization between these taxa.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 443–451.